The Camera

A camera is a light tight box with a hole in one end to let the light in. Hold on to this thought.

We believe that the easiest way to explain things is with a brief history, but if you don't agree, go down this module to
the heading 'A Snapshot Camera'.

Basic camera (with lens)

Because the light rays cross over in the lens, the image is always upside down.

A Brief History

A camera doesn't even need a lens -- you've heard of pinhole cameras -- and it doesn't need film or a digital sensor.
The original 'camera obscura' (literally, 'darkened room') was known at least 1000 years ago: it was taken for granted in
Alhazen's Book of Optics in the 11th century.

The Tudor House, Margate

Shot with a Rigby pin-hole camera on 4x5 inch Polaroid Sepia film. This camera doesn't have a viewfinder,
just sighting lines (marked by brass studs) on the top and side of the camera. These give a surprisingly accurate idea of
what will appear in the final image.

At its simplest, a camera obscura is a darkened room with bright sun outside; a small hole in a shutter
over the window; and a white-painted wall opposite the hole. On the wall, you'll see an upside-down image of the scene outside.

It won't be very sharp, but it will be recognizable, even if the 'pinhole' is big enough to stick your finger through. In fact
it will have to be big enough to stick your finger through, or you won't get enough light to see the image. Add a lens, as
Daniello Barbaro described in 1568, and the image can be made a lot brighter and sharper (but still upside-down). Hang
light-sensitive material on the wall, and you can take a picture.

Rigby pinhole camera

This is the camera that was used to make the picture above -- and indeed, there is another view of the Tudor House in the
stack on the left. The (rather indistinct) black lump protruding from the top of the camera is the Polaroid 5x4 inch film
holder that is needed for shooting peel-apart Polaroid films.

The round bit at about one o'clock from the lens is the shutter. It pivots around the pin just next to the black circle
with the brass pinhole plate in it. There is no provision for focusing, because pinhole cameras don't focus. Everything, at
any distance, is equally sharp (or unsharp).

A photographic camera is rarely room-sized, though it can be. The most important difference between a photographic camera and
a room-sized camera obscura (preferably with lens, as described above) is a way to control the length of time the light shines on
the sensitive material: the camera shutter.

Too short an exposure, and not enough light will fall on it to make a picture. Too much, and the whole thing will 'fog' from an
excess of light. Just right, and you can record an image. 'Just right' isn't very critical, at least with negative film: the maximum
amount of light you need before image quality suffers too badly is maybe ten or even twenty times as much as the minimum that gives
a recognizable image. This is the way that simple snapshot cameras work: quite a wide range of exposures gives acceptable results.

The film or plate holders (stacked behind the camera) are substituted for the focusing screen on the back of
the camera. This is taken from an Ilford Manual of Photography of 100-120 years ago. There's a free module about
loading cut film holders (with pictures of the light-trapped slides) in
'How Do I...?

In the early days of photography, sensitive materials were so slow that exposures ran into many hours, though this was
soon reduced to minutes and then to seconds. For decades, the photographer's hat was entirely satisfactory as a shutter.
The drill was as follows. Insert the sensitive material in a light-tight holder; hold your hat over the lens; pull back the
light-trapped slide that covers the film or plate inside the camera; remove hat; count to twenty (or whatever) and replace
hat. Push the light-trapped slide back in, and you have your picture.

This is the way that large format cameras work to this day. There is a sheet of ground-glass on the back. The photographer
opens the shutter (the modern version of his hat); focuses and composes the picture on the ground glass; closes the shutter;
inserts the film-holder; pulls back the dark-slide; opens the shutter for the necessary time to give the correct exposure;
and replaces the dark-slide.

Clearly, the substitution method is not particularly convenient. A much easier way to do things is to have a roll of
light-sensitive material in the back; some way of winding it on by a fixed amount for each exposure; a shutter in the
front; and some way of aiming the camera so that you can guess what is going to be on the sensitized material when you
make the exposure. Then all you have to do is aim; press the shutter release; and wind on to the next frame. This was
the basis of George Eastman's Kodak in 1888, the world's first commercially successful mass-market snapshot camera. It
came ready-loaded with 100 exposures, and when you had used them all up, you sent the camera back to Kodak to have your
pictures made. They were returned to you with the reloaded camera. As Uncle George said, 'You press the button, we do
the rest.'

Viewfinders

On the left (1), a simple frame finder. In the centre (2), the misleadingly named 'brilliant finder'
used in so many box cameras. Brilliant, possibly; finder, barely. On the right (3), a basic reverse-Galilean finder of
the type still used to this day in single-use cameras. These and other illustrations are stolen wihout apology from a
Soviet-era photography book. Well, the Soviet Union never believed in copyright...

A Snapshot Camera

The simplest cameras available today are so called 'disposable' or 'one time use' cameras, and they are surprisingly similar
to the 1888 Kodak. The biggest difference is that they use smaller film, which is enlarged to make a print, whereas original
Kodak films were contact printed, that is, sandwiched against a piece of light-sensitive paper and exposed to daylight in order
to to make a same-size print.

As we said at the very beginning of the module, the camera is a light-tight box. The single-use camera is no exception.
There's a lens at the front: a simple plastic lens, not very sharp, and 'fixed focus' or 'focus free'. There's a shutter
behind that, with a single speed, typically around 1/50 second. There's a roll of film, and a simple wind-on counter, at
the back. On top, there's a simple viewfinder, a couple of plastic lenses again. And that's about it. Fancy models may have
an electronic flash, but this is far from essential.

Kodak Max HQ Single-Use Camera

All right, it's got a built-in electronic flash, and it's quite a fancy model, but under the skin it's a very simple
camera. The viewfinder is Type 3, above.

Actually, our grandparents' box cameras were pretty similar to a modern single-use camera. The main difference is that
they used bigger film (contact printing again) and that they were user-reloadable. For that matter, a basic modern digital
camera (including camera phones) isn't that different, except that the film is replaced by an electronic sensor and the
shutter is electronic. It doesn't open and close: it just tells the camera when to 'freeze' the image on the sensor.

Box camera

The big nickel key winds the film on; the numbers on the backing paper (see the free
handling 120 film module in How do I...?) appear in the red window on the back.
This camera probably dates from the 1920s or 30s and has 'brilliant' finders (type 2, above).

The disadvantages of snapshot cameras

It is often said that a good photographer can get better pictures with a snapshot camera than a bad photographer can get
with a good camera. Well, yes, sort of. But the drawbacks are considerable.

To start with, the picture won't be very sharp. The lens is simple and of low quality, and the focus is factory-set to
give acceptable sharpness across a limited range, typically around 2 to 5 metres or 6 to 15 feet. You can't do close-ups,
and distant subjects may not be all that sharp either. For better quality, you need a more complex (and therefore more
expensive) lens, and some way to vary the focus. There's another basics module on
lenses.

Second, it will only work in good light (unless it has a flash, of course). The lens does not let much light through.
A 'faster' lens will let more light through, but again it costs more, and besides, faster lenses mean that some way of
setting focus isn't just desirable: it's essential. This is to do with
focus and depth of field, which is, yes, the subject of yet another free Basics module.

Artie and Marion Schultz, 1959

Frances was 13 or 14 when she took this picture of her parents with a fixed-focus 127 box camera. Even at
this size, you can see that it isn't very sharp, and there's not much detail in the shadows, even out of doors on an
overcast day.

Third, the fixed shutter speed introduces limitations of its own. It won't be fast enough to 'freeze' motion, and it won't be
long enough to allow really long exposures for low light. Guess what: there is another Basics module on
shutters and speeds.

Fourth, there's no choice of lenses: no wide-angles to 'get more in', no telephoto lenses to pull up detail from afar. There's
more about this in the module on lenses.

More Versatile Cameras

To get better pictures we need some or all of the following: a better lens, a way to focus it, a controllable shutter, and
(ideally) either a choice of lenses or a zoom lens: both of the latter have their advantages, as discussed in the free Basics
module on lenses.

For exposure and focus, we have a choice of automation or manual control. Obviously automation saves you having to think
about what you are doing, or needing to learn how the camera works, but it seems a fair assumption that if you have read this
far, you probably want to know a bit more about what the camera does so that you can decide whether to let the automation do
the work, or do it yourself. You probably also want to know a bit about digital versus film.

Nikon F

Arguably the greatest single-lens reflex (SLR) of all time, the all-mechanical, totally manual Nikon F was introduced in
1959 with a wide range of superb lenses and a shutter from 1 to 1/1000 second plus B and T (shutter stays open until you
close it).

Manual and automatic focus

The simplest form of manual focus is by scale. There is a focusing scale (normally but not invariably on the lens) and you
set an index mark against the focused distance. Of course you have to guess or measure the distance, but it's surprising how
accurately you can guess with even a minimum of practice.

Alternatively, you can focus via substitution (swapping between a film holder and a ground glass, as described above); via
a rangefinder, which can be either coupled to the camera focusing or uncoupled; or via a reflex screen. There's more about all
of these on the right and below.

The principle of the uncoupled rangefinder

The photographer looks through a fixed semi-silvered mirror or prism, 1, directly at the subject.
At the same time, he sees a second image of the subject reflected from the moving mirror, 2, which rotates on a pivot,
3. A pointer, 4, indicates the distance on a scale, 5. The longer the rangefinder base (the distance between the two
mirrors), the more accurate the rangefinder can be.

A coupled rangefinder

By coupling the swinging mirror to the focusing mount of the lens, the rangefinder can be made to set the lens
at the same time as you focus; they called this 'automatic focusing' in the 1930s. 1, lens; 2, coupling cam;
3, actuating lever; 4, moving arm for swinging prism; 5, swinging prism (replaces the mirror in the diagram above)
just above pivot; 6, semi-silvered mirror; 7, stop so that you only see the centre spot from the right-hand window.
The rangefinder and viewfinder can be combined, and usually have been since the 1950s.

Autofocus

Autofocus can be active or passive. The classic active autofocus uses sonar (bounced sound waves) to gauge the subject
distance, while passive autofocus normally works by contrast: the in-focus image is the contrastiest. According to all the
studies we have seen, careful manual focusing is more accurate and more reliable than autofocus. It is much more disputable
which is faster. The best, fastest autofocus systems are probably faster than most people can focus.

On the other hand, manual focusing allows you to pre-focus on a set point, and shoot -- with no focusing delay
whatsoever -- as soon as everything comes right in the viewfinder. This is a traditional sports photographers' trick. After
all, you know that barring severe mishap, runners will pass a certain point, pole-vaulters will go over the bar, and so
forth. There's a free module about zone focusing and pre-focusing.

Zorkii-4K

This simple Soviet-era rangefinder camera has its eccentricities -- there is a 'forbidden zone' in which you will break
the shutter if you rotate the dial, and you have to lift the dial before you can twist it -- but countless superb photographs
have been taken with these cameras.

Circus horse, Kelvinhall Circus, Glasgow

Even a fairly basic camera with slow lenses and slow film can be surprisingly versatile. Roger
shot this in about 1970 or 71 with a 1936 Leica IIIa, an even older 90mm f/4 Elmar lens, and 50 ASA slide film
(called Barfen -- honestly!). The old ASA film speed scale formed the basis of the modern ISO arithmatic film scale.
As you can see, he needed a very long (hand-held) exposure, maybe 1/4 second, even at full aperture. There is both
camera shake (a loss of overall sharpness -- look at the lights) and subject movement. Flawed? Yes. But still rather
an entertaining photograph, a good memento, and a lot better than no picture. With modern ISO 200 film and an f/2.8
lens, he could use 1/30 second for the same exposure. The rule of thumb for hand-holding a 90mm lens on 35mm suggests
a minumum exposure of 1/90 second. Never be afraid to ignore guidelines.

Another useful trick you can do with manual focus, which is impossible with autofocus, is zone focusing. This is such a
useful technique that it has its own little free module in the 'How do I...?' strand. Basically, it's a jumped-up version of
the fixed focus technique used in disposable cameras, and it allows you to walk around with your camera pre-set at the distance
at which you expect to take pictures. You might care to pop over to the Zone Focus module
and then come back here -- or you might care to leave it until later.

Exposure control and automation

There are two ways to control the amount of light falling on the film or digital sensor. One is via the size of the hole
the light goes through -- the aperture -- and the other is the length of time the shutter is open.

Iris diaphragm

The multiple metal leaves -- eight in this case, but it can be more or less -- open and close to create different
sized apertures. Many people find that more leaves, and a more perfect circle, give a better quality to the out-of-focus
image, the so-called 'bokeh'.

Broadly, aperture opening and shutter speed are interchangeable. If you let twice as much light through the lens, you
can afford to halve the exposure time, or if you give ten times the exposure time, you can afford to reduce the amount of
light going through the lens by a factor of ten. This rejoices in the name of the Bunsen-Roscoe Reciprocity Law, though
very few photographers know its full name. At very long exposure times it breaks down -- 'reciprocity failure' -- and you
have to give more exposure. This varies with the film: some require no extra exposure at 10 seconds, while others require
50 per cent more at 1 second. It also breaks down at very short exposures, typically 1/10,000 second and less.

If you control exposure yourself, you have to set both shutter speed and aperture. You can choose a fast shutter speed
to 'freeze' action, or a slow shutter speed, either to create blur or because there is so little light around that you have
no real choice. And you can choose a wide aperture or a small one, though the effects of choosing these are more complicated
and are explained in the focus and depth of field module.

The iris diaphragm of an old Ross brass lens

Samoca controls

On this 1957 Samoca LE you can see the focusing mount (focus set to infinity, with a focusing nub at about two o'clock
in the picture -- turn it clockwise, as seen from here, to focus closer); the aperture settings from f/2.8 to f/22, here set
to f/5.6 (notice that the stops are not equidistant, which is normal in cheaper or older cameras); and the shutter speed dial,
here set to 1/25 second from a range of 1 to 1/300.

The '1/300' speed would probably have been doing well if it was 1/250 when new, and half a century on, 1/200 would be
nearer the mark. Shutters are only expected to be within about +/- 30 per cent of their nominal values, even when new, so
there is no sense in looking for more precision than is likely to exist.

A half-way house between manual exposure and full automation is to set either the shutter speed ('shutter priority') or the
aperture ('aperture priority') and let the camera's automation choose the other. This is fine unless you need to set an exposure
that doesn't agree with the meter reading.

With full automation, you just let the camera decide both the aperture and the shutter speed, according to criteria laid
down by its designer. This is fine for many kinds of photography, again subject to the meter giving you the best exposure
(which it won't always), but there will be times when in order to get a specific effect you will need to take control for
yourself. For example, if you want a very long exposure to capture subject movement, you will rarely find that the camera
sets what you want, and if you want a very wide aperture so that the subject is in focus and the background is out of focus,
it probably won't do that either.

Actually, many cameras offer a wide choice of exposure 'modes', including fully manual, aperture priority, shutter
priority, and various auto modes to favour action freezing (often called 'sports mode'), deep focus from front to back
(sometimes called 'landscape mode') and so forth. Our own view is that when you are faced with this many modes, it's
often easier as well as more rewarding to take control for yourself, rather than trusting the camera.

Ice Skater

What 'mode' would you use here? Surely it's easier to use a long shutter speed that you know will blur the image, and
set the aperture accordingly (or use 'shutter speed priority' automation, above). If you don't know what sort of shutter
speeds cause what sort of blur, just experiment. This is probably about 1/15 second, or maybe 1/8 (Roger took it a very
long time ago, when you could still take pictures at ice-rinks in England without being arrested) but it would be
interesting to try everything from 1/30 to 1/4 or so. You'd also learn a lot more than you would if you relied on the
camera to do everything for you. This was almost certainly shot with a Nikon F, but the lens is long forgotten: maybe a
58/1.4 Nikkor. Film was Ilford HP5 (in pre-HP5 Plus days) printed on Ilford paper.

Digital and film

At the top end of the market -- the price of quite a good motor-car -- you can get some truly amazing digital cameras. At
the more affordable end of the market, especially if you buy second-hand, you can buy a 35mm film camera that will wipe the
floor with digital, at a fraction of the price: an old Nikkormat SLR, often at less than £75/$150/120 euros, or even
a fixed-lens rangefinder camera like our old Konica III at £20/$40/30 euros, has the potential to deliver far better
quality than most new digital cameras at £300-600, $500-1000, 400 to 800 euros.

Perhaps more to the point, film and digital have a very different look from one another. Digital often has a sort of
airbrushed perfection to it. This suits some subjects very well -- flattering portraits, for example -- but looks rather
unreal for others, including reportage, landscapes and wildlife. You can't really compare the two on-screen, on a site
like this: you have to see them side by side, as prints, and decide which suits you better.

Pentax SV with 135/1.8 Porst

Porst is a big German retail chain, and this is a rebadged Soligor from the 60s or 70s. Objectively it
is a lousy lens, soft and flary. But it's also dirt cheap (if you paid £60/$100/80 euros, you'd be ripped off), and
it gives unique effects thanks to its very high speed for its focal length (the standard Pentax 135mm from the 1960s was
an f/3.5).

If you like the effects the old Porst gives, you can take superb pictures for next to nothing: a used
camera body that accepts M42 fit lenses can be had very cheaply. A black 1960s SV like this might attract the attention of
collectors, but a chrome version of the same body could probably be found for £20-30, $40-50, 30-40 euros. Yes, you
have to learn to use an exposure meter, but that isn't difficult -- and you don't have to learn to use it very accurately
if you are shooting colour negative film.

Formats

There's an old saying in photography, borrowed (as far as we know) from boxing. It is that a good big 'un will always beat a
good little 'un.

In other words, a bigger film area or a bigger image sensor will always deliver better quality. The most usual formats in
film are 35mm and 120 roll-film.

The standard format on 35mm is 24x36mm, though 'half frame' (18x24mm, also known as 'single frame' because it is the old
movie format) was popular in the 1960s.

Bistro, Paris

You can get surprisingly high quality from 35mm, especially if you use a tripod. Frances shot this on
Fuji RFP ISO 50 with a Nikon F and 35/2.8 PC-Nikkor

Roll film

A range of formats is possible on 120 (roll) film. This was originally designed for use in snapshot cameras at the beginning
of the 20th century, but it was a widespread professional standard from the 1950s to the present day. It is fast yielding to high
end digital in the professional realm, partly for speed -- the film doesn't have to be biked to the lab, processed, and biked
back -- and partly for cost: if your bill for film, couriers and processing is hundreds of pounds, euros or dollars per week, it
quite soon makes sense to spend £20,000, $35,000 or 30,000 euros on a Hasselblad 39-megapixel camera. It's not really about
quality: roll-film is as good, or better, in that respect.

A roll of exposed 120 film

The backing paper is secured by a lick-and-stick tape, which betrays the antiquity of roll film. This is from the free
'How Do I...?' module on handling 120 roll film.

The various roll-film formats are generally known by their nominal sizes, but they are actually rather smaller, as shown in
the table. One dimension is set by the width of the film (which is 62mm, not 120mm), and the other can be varied.
Indeed, there are panoramic formats obtained by doubling up 6x6 to get 6x12 and 6x9 to get 6x17. Both [cm] and [inches] are
in square brackets because the actual units are rarely mentioned: you're supposed to know that 'two and a quarter
square' is inches, while 'six-nine' is centimetres.

Nominal size

Dimension across width of film

Dimension along length of film

Number of shots on standard 120 roll

645, 6x4.5 [cm]

55-56mm

40-43mm

15-on, rarely16-on

6x6 [cm], 2¼ [inches] square

55-56mm

55-57mm

12-on

6x7 [cm], 2¼ x 2¾ [inches]

55-56mm

65-72mm

10-on, rarely 9-on

6x9 [cm], 2¼ x 3¼ [inches]

55-56mm

78-84mm

8-on

Attic

When you want to capture a lot of detail and texture, 120 film allows you to do so a lot cheaper than
digital. This is from a Linhof 6x7cm transparency (56x72mm) exposed using a modified Linhof Technika 70 camera and (as we
recall) a 105/5.6 Schneider Apo Symmar lens. You could buy the camera, an equivalent lens and a back, second-hand, for under
£1000/$2000/1500 euros. A 39-megapixel Hasselblad will give equivalent quality at over 20x the price...

Digital formats are barely standardized at all -- which is not at all unusual in electronics. As the saying goes, the great
thing about standards in electronics is that there are so many to choose from. The smallest sensors are found in point-and-shoot
and 'bridge' cameras (so called because they are supposed to bridge the gap between snapshot cameras and serious 'enthusiast'
cameras), while the biggest are found in so-called 'medium format' cameras such as the Hasselblad mentioned above. In between
there are 16x24mm sensors, as in most Nikons; 18x27mm sensors, as found in the Leica M8; 'full-frame' 24x36mm sensors...

The advantage of a bigger sensor is that the pixel density can be lower, and this allows higher quality: the image signal
has to be amplified less, resulting in less 'noise' (image degradation). On the other hand, bigger sensors cost more money,
and it's easier to build lenses to deliver the kind of very high resolution that is needed if the sensor is smaller, so there
are arguments on both sides.

Bicycle in the back yard

This was one of our earliest shots with the Nikon D70, using a 90/4 Dreamagon soft-focus lens. Because the sensor in the
D70 is 16x24mm, the Dreamagon gives the same coverage as you would get from a 135mm lens on full-frame 24x36mm 35mm film.
Although the D70 is only 6 megapixels, they tend to be higher-quality pixels than 8 megapixels on a smaller chip.

How many pixels equates to what size film?

Alas, this is all but impossible to answer, because it depends too much on chip size (above), subject matter
(film does better with highly detailed subjects) and the way the camera is used (hand held or on a tripod). Even
so, here's a good working guide.

With the best 35mm cameras, lenses and film available, used under ideal conditions, with the camera on a tripod,
reliable estimates range from 18 megapixel equivalent to over 30 megapixel equivalent. The latter came from a
software-writing acquaintance who gave as an example of a demanding subject 'a portrait of Art Garfunkel with
every hair sharp'.

For hand-held reportage, again with top-quality 35mm, the equivalent is anything from 14 megapixels downwards.
Probably 10 megapixels is all you need under most circumstances, and 6 megapixels (from a decent-sized chip) should
be OK for weddings.

London Eye

The 15mm f/4.5 Voigtländer Super-Wide-Heliar that Roger used for this shot gives the same
angle of view on the 18x27mm sensor of the Leica M8 (which is where he used it) as a 20mm lens on full-frame 24x36mm
film. In all probability, the 10 megapixels of the M8 at ISO 160 equivalent captures about the same information in
this hand-held shot as he could have got with his Leica MP, a 21mm lens and ISO 100 Kodak Elite Chrome EBX.

Camera Types

There are many ways to classify cameras, but one of the easiest (and for somewhat oblique reasons, one of the most useful)
is according to their viewfinders. The most basic type is the viewfinder or direct-vision camera, where the finder is no more
than a wire frame or small optical finder that indicates the field of view, usually not outstandingly accurately. Actually
there is an even more basic type, where there is no viewfinder at all, just sighting studs or even stamped or moulded lines
on the top of the camera, but this is pretty rare nowadays.

Focusing with direct-vision finders (where it is available at all) may be automatic, or by scale, or by coupled
rangefinder (a paid module). This last kind of camera has enjoyed something of a renaissance
since the late 1990s, because the cameras are (or can be) small, light, unobtrusive, quiet and with very high quality lenses.

Bilora Bella direct-vision camera

The Bella is a sort of jumped-up snapshot camera with a slightly better lens and limited controls. There's a simple
optical finder, represented by the hole in the front above the lens, but as you can see from the front of the lens you
can focus (by scale) from 1 metre to infinity. At about 7-8 o'clock on the lens you can see the '11-8' setting for f/11
and f/8, and although you can't easily see it here, a shutter speed control on top of the lens gives you 1/100 second,
1/50 second and 'B', where the shutter stays open as long as you hold it open.

Historically, the substitution method of focusing and composition is even older than direct-vision viewfinders,
though more complex. It goes back to the dawn of photography and has already been mentioned: the sensitive material
(one sheet at a time, or in a roll-holder) can be interchanged with a ground-glass viewing screen.

Imperial 11x14 inch

With very large format cameras, the ground-glass on the back is almost like a television screen: this
one is 11x14 inches, roughly equivalent to a 19-inch television screen. It is easy enough to focus directly on it with a
low-powered magnifier, though unless you are working in a darkened studio with only the subject brightly lit, you need to
exclude ambient light with a focusing cloth.

You only need a low-powered magnifier, because you aren't likely to enlarge an 11x14 inch negative by
much. Or indeed at all: contact printing is much more usual at 5x7 inch/13x18cm and bigger.

After direct-vision and substitution comes the single-lens reflex or SLR, so called because the same lens
is used for both the viewfinder and the final picture: the Nikon F and Pentax seen elsewhere in this module are SLRs, as
are the (35mm) Exakta seen on the left and the (roll-film) Kowa seen on the right. SLRs are generally held up as the
nearest thing there is to a 'universal' camera but this is not the same as saying that they are invariably the best
camera for any specific application.

There is a schematic of the SLR layout just below. A mirror (hence 'reflex') reflects the light onto a focusing screen,
then swings out of the way to allow the light to reach the film or sensor. A few very basic SLRs use the mirror as the
shutter, but most have a separate shutter behind the mirror. There is an inevitable brief blackout while the picture is
being taken, except with a few very specialized cameras that use a fixed, semi-silvered beamsplitter mirror.

Fourth, and very rare nowadays, is the twin-lens reflex or TLR. This consists in effect of two cameras linked together.
The lower camera takes the picture; the upper camera is a reflex and is used only for focusing. Again, a schematic diagram
is given below.

Graflex 22

In keeping with the (somewhat sloppy) American practice of naming formats to the nearest quarter inch, this 2¼ inch
square TLR is known as a 'Graflex 22'. It dates from the 1950s, the glory days of TLRs, though the greatest of them all, the
Rolleiflex, was introduced in the 1920s. Almost all TLRs use 120 film, and the vast majority are 6x6cm, though there have been
35mm models; 127 models (a small, obsolescent roll-film size resembling scaled-down 120, 46mm wide); and even 4x5 inch and 5x7
inch models, though these are BIG.

Reflex viewfinders

On the left, A, is a simple single-lens reflex. In the centre, B, is a twin-lens reflex. With both SLRs and TLRs with
direct viewing of the ground-glass, the image is the right way up but laterally reversed ('flopped' left-to-right). This
can make it hard to follow action... On the right, C, is a single-lens reflex with pentaprism viewing for a right-way-up,
right-way-round image.

The fifth and latest entrant is the electronic viewfinder, which may be a screen on the back of the camera or an internal
screen (on a 'bridge' camera). Because it is difficult or impossible to focus using a small LCD screen, most electronic-viewfinder
cameras use automatic focusing only.

Spatial parallax

With electronic viewfinders, substitution (ground-glass) viewfinders and SLRs, you see pretty much what the film or sensor
will see, though there is often a slight discrepancy in area (the finder usually shows less than the film or sensor will capture)
and there may be small failures of alignment, i.e. the viewfinder is offset up, down, left or right as compared with what the
sensor sees.

With direct vision cameras and TLRs, there is inevitably a small distance between the viewfinder window/viewing lens and
the taking lens, and the closer you focus, the more important this becomes. Down to a couple of metres, about six feet, it
hardly matters at all, but closer than this, you may have to make allowances. Some viewfinders have a supplementary dotted
line below the top frame, to be used at 1 to 2 metres or 3 to 6 feet; some cameras have moving brightlines; some TLRs have
moving masks; some supplementary finders can be tilted manually to compensate for parallax. True compensation is impossible,
because the viewpoint is slightly different, but for almost all practical purposes, parallax-compensated finders are
accurate enough.

Graflex 22 Sports Finder

In common with most TLRs, the front of the viewfinder hood on the Graflex TLR pushes down to make a
'sports' frame finder in conjunction with a peep-sight in the back of the hood. This is obviously even further from the
optical axis of the lower (taking) lens than the upper or viewing lens, but it is normally used only at distances of
3-4 metres/10-12 feet or more. It is amazing how imprecise many viewfinders are -- and it is still more amazing how
little this seems to matter. The sports finder makes it much easier to track moving action, instead of using the
laterally reversed viewing screen.

Another point contributing to the inaccuracy of separate viewfinders is that the angle of view of a lens decreases
slightly as it is focused closer. A brightline of fixed size can therefore be accurate only for a single fixed distance.
The vast majority of direct vision cameras, including the best 35mm models on the market, simply ignore this problem, though
they do play safe by showing a bit less than will appear on the film or sensor. There is however at least one (the Linhof
Technika 70, a long-discontinued roll-film camera) with projected brightlines that move for parallax compensation and get
slightly smaller as they do so in order to compensate for the angle of view.

Temporal parallax

This sounds pretentious but we have never heard a better way to describe it. Basically, it's the delay between pressing
the shutter release, and taking the picture. With the very fastest-responding cameras, including most manual TLRs and many
direct-vision cameras, it can be 20 milliseconds or less. With 35mm SLRs, where the mirror has to swing out of the way before
the shutter can open, 30-60 milliseconds is likelier; early auto-exposure cameras were often slower still. With roll-film SLRs
it can easily hit 100 milliseconds, 1/10 second: a friend of ours reckoned that the first time he used his new Hasselblad at
a motor-racing meeting, he had lots of pictures of the back ends of cars disappearing out of the picture.

Blind-side break

When you are shooting sports and action, a fast responding camera is very important indeed. Roger was testing a
300/2.8 lens for the British Journal of Photography when he shot this on a dull, wet afternoon (typical rugby weather,
as he recalls from his schooldays), using as far as he remembers 'pushed' Ilford HP5 (rated at 1000). The camera was an
elderly Nikon F. Focusing was completely manual. Fast lenses are easier to focus as the image snaps in and out of focus
more quickly. This is as true with autofocus as with manual focus. We are not sure what a blind-side break is, but it's
the way the BJP captioned it and it sounds very technical so we left it.

The best autofocus cameras are now very fast indeed (though not as fast as pre-focusing, as described above) but the worst,
especially some digital cameras, are very slow indeed, a substantial fraction of a second and even in some cases a second or
more. This can seem like forever if you are used to cameras that take pictures when you want them to.

Three Stupid Questions

It is comforting to think that there are no stupid questions, only stupid answers, but stupid questions do exist. Stupid
questions are those where a moment's thought would reveal that you already know the answer, or that you could easily work it
out from information already available: unless you really are stupid, the only reasons you would ask such questions is because
you are too lazy to think, or because of 'hardening of the categories'.

All three of the stupid questions below fall into the last category: because people are used to battery-powered cameras with
battery-powered meters, they assume that all cameras fall into both categories. They don't, of course.

1: Where do the batteries go?/What batteries does it take?

This is only a stupid question if the camera is fully mechanical and has no meter. The answer, of course, is that it doesn't
take batteries. It may also be that the camera has a selenium-cell (photogenerative) meter, which, as its name suggests,
generates the power for the meter from the light falling on the cell. Once you have seen a selenium cell, a big, flat thing
that is quite unlike the small window for a CdS or other photoresistive meter, you can usually tell which meters need batteries
and which don't.

Leica IIIa with 90/2.2 Thambar

No meter and a fully mechanical shutter (what do you expect in 1936?), therefore no batteries or film speed setting. The
very rare Thambar soft-focus lens dates from maybe 1938 but the Tewe zoom finder on top is much newer, dating from the 1950s.

Selenium meter cell on Samoca LE

Yes, the camera has a meter -- but its relatively huge area and dimpled front tells you it's a selenium (photogenerative)
meter that doesn't need batteries. The trapdoor cuts down the light under very bright conditions and also helps preserve the
meter: old selenium cells often die of exposure if left uncovered.

2: How do I set the film speed?

Again, this is only a stupid question if the camera has no meter, in which case it does not take long to work out that the
only reason you need to set film speeds is to tell the meter what sort of film you are using, and if there's no meter... Some
cameras do have film reminders, though: see the free How Do I...? module on
Using 35mm Cameras for an example.

3: What happens if I take the batteries out?

The sub-text here is, 'Will the shutter still work, or will it only be the meter that dies?'

Well, try it. You'll get a much quicker answer than you will by asking someone else...

Voigtländer Bessa-T with Russian turret finder

Yes, this one does take a battery. Two SR44/LR44 batteries, in fact. Take them out and the meter stops working. The
mechanical shutter doesn't. It will take you two minutes or less to discover this by experiment.

The Bottom Line

It may seem that there is an awful lot to think about and remember, but really, it's not that complicated. After all,
120-format box cameras were introduced over 100 years ago and were used without great difficulty by innumerable snapshotters,
and 35mm is easier still. Besides, you don't have to master everything at once. You can often treat even the most expensive
and versatile cameras as box cameras to begin with, using a single shutter speed and a single aperture, leaving only the focus
to worry about (and if you use zone focusing you needn't even worry about that). In fact,
there's a module called The Box Brownie Leica (though it's not just about Leicas).

Chapel roof, Greece

Photography is about enjoying yourself, and trying things, and not worrying too much if they don't work. Roger set the
camera on the floor for this picture, pointing straight up. He focused by guesswork and bracketed
(free module) the exposure, giving two or three different exposures to see which would work best. There's no extra lighting
or flash: just what was in the chapel.